Pure Asynchronous Tasks in Javascript

Question

Combining Ramda and Folktale functors

_fetchLists is a function that performs an async operation, it takes the following arguments:

1. fetchAlllists: an async function that resolves with Result functor of an array of list objects

2. listIds: an array of listIds

   it returns a Result functor of an array of list objects

   • Is _fetchLists considered a pure function?
   • fetchAlllists is implemented to return a promise that resolves with a Result, is there a benefit from using Task functor instead of normal promise?

const _fetchLists = R.curry(
  async(fetchAllLists, listIds) => {
    const lists = await fetchAllLists();

    return R.map(
      R.compose(
        R.values,
        R.pick(listIds),
        R.indexBy(R.prop('id'))
      ),
      lists
    );
  }
);